This is a great shot, Tejal! I especially like how you got down low at eye level with your subject. I can only restate what others have already said about the image; the boy's concentration, the action of the marbles motion, etc.
The image does not look quite sharp to me, so I had a look at the full-size one on your Flickr site and that confirmed this lack of sharpness. At f/5 on your lens, I would guess that the shot is at full aperture? The 1/500th sec should freeze the motion. My guess is that the camera focused in front of the boy, likely on the marbles on the ground. Out of focus can't be fixed, but I tried a bit of sharpening to see if it might help a bit.
I also found that lifting the shadow detail opens up the boy's face and body a bit and I think that helps a bit too. I also agree with the others that suggest that the marble flying through the air on the left is distracting, so I cloned it out and I also found I agreed with the people who felt the boy was too centred, so I cropped to increase the asymmetry in th e shot a bit. Here is my edit: